1. Field of the Invention
This invention relates to a universal shot wad that provides precise control of an adjustable volume available for the shot columns of a wide range of shot shell loads. More particularly, the combination of an adjustable shot cup base interengaged with a shot sleeve provides the desired volume. Apertures extending through the sides of the shot cup base cause sidewall portions to flare outwardly when expelled from a shotgun muzzle. The flared sidewall portions increase aerodynamic resistance of the shot cup base causing the shot cup base to rapidly separate from the shot string thereby minimizing disruption of the shot flight pattern.
2. Description of Related Art
Shot shells containing shot to be expelled from a shotgun have a hollow cylindrical, typically plastic, husk sealed by a base cap at one end and a crimp at the other end. Contained within the shot shell are a powder charge adjacent to the base cap, a plurality of shot adjacent to the crimp, and a shot wad separating the shot from the powder charge. Conventional shot wads consist of three parts: a powder cup, a shot cup and a compressible section between the powder and shot cups.
The powder cup retains the powder charge confined within the shot shell load and seals the gasses generated on powder ignition. Efficient gas sealing is important to achieve consistent load velocity and pressure performance. The shot cup encapsulates the shot column to protect the gun barrel as the shot column travels down the bore. The compressible section of the shot wad provides an element of adjustibility in the wad to accominodate variations in shot size, powder charge weights and/or density and to provide a snug load fit. On firing, the compressible section collapses to increase the available volume for expanding gases. This reduces the peak pressure required to achieve a specified velocity.
A shot receiving portion volume is usually sized to a specific shot weight for a limited range of shot sizes. Multiple shot wads of different sizes are required for the wide range of commercial loads and shot weights. While this approach is effective, it is also expensive.
U.S. Pat. No. 2,144,232, that is incorporated by reference in its entirety herein, discloses annular grooves on an inside wall of the husk at the open end, opposite the base cap. After shot are loaded, a closure disk engages one of the annular grooves retaining the shot.
Another approach, disclosed in U.S. Pat. No. 3,730,095 to Lage, that is incorporated by reference in its entirety herein, discloses a shot cup having deformable legs that contact an over powder cup. When shot are loaded into the shot receiving portion, the open end of the husk is crimped to form a seal over the shot. The legs of the shot cup deform as necessary to provide a snug fit for the shot.
U.S. Pat. No. 3,788,224, that is incorporated by reference in its entirety herein, discloses a multiple piece adjustable wad system having a powder cup with a collapsible post and a series of shot cups with fixed volumes. This adjustable wad system provides a means to compensate for the variability of powder density, powder charge weight and shot weight. The system has the disadvantage of requiring a large number of components for a wide range of loads. For example, in 12 gauge 23/4 inch loads, this wad system would require six different shot cups, in addition to the powder cup, to accommodate a shot weight range of from 7/8 ounce--15/8 ounces. As described below, the present invention accommodates the same weight range with a two piece system.
In another approach, a shot sleeve is slit in four locations to form flexible sidewall portions and then inserted into the shot shell. The length of the slits is to the desired location of the bottom of the inserted shot cup base. The shot sleeve is a tubular member having an open end adjacent to the open end of the shot shell and a closed end forming the powder cup. The inside wall of the shot sleeve is substantially smooth adjacent to both the open end and the closed end and contains a plurality of substantially parallel, inwardly projecting, first ribs circumscribing the inside wall between the two smooth portions. A cylindrical shot cup base having a ribbed outer surface that interengages the ribs of the shot sleeve is then inserted to a desired depth to form a shot receiving portion shot cup of the appropriate volume.
This "universal" shot wad provides a very effective fit for a wide range of loads. On firing, the shot cup sleeve and shot cup base are expelled from the shotgun muzzle with the shot. The slit shot sleeve petals open increasing the aerodynamic resistance causing the shot sleeve to rapidly drop away from the shot string.
The cylindrical shot cup base, having less aerodynamic drag than the sleeve, travels with the shot string for a longer distance and tends to interfere with shot flight pattern. In lower shot weight loads, such from 7/8 ounce to 11/8 ounces, the volume of the shot column captured within the shot cup base is a relatively large proportion of the total shot column. Therefore, any adverse influence by the shot cup base on the shot string is more pronounced in these light weights.
While it is known to form longitudinally running slits in shot cups to cause sidewall portions to petal open when the shot cup is expelled from the muzzle of a shotgun increasing aerodynamic resistance and causing the shot cup to lag behind the shot string, as disclosed in U.S. Pat. No. 5,361,700 to Carbone, presently utilized longitudinal slits are suitable for the shot sleeve, but not for the shot cup base. In the universal shot wad, the shot cup base is inserted with considerable force into the shot sleeve to interengage with the ribs of the shot sleeve. Longitudinal slits, as presently known in the art, significantly weaken the strength of the shot cup base sidewalls causing them to be prone to distortion when inserted into the shot sleeve and interfering with proper interengagement between the shot sleeve and the shot cup base. Also, longitudinal slits do not provide sufficient flexibility for the short sidewalls of the shot cup base.
There remains, therefore, a need for a shot cup base suitable for use with a ribbed shot sleeve that provides sufficient aerodynamic resistance so as not to interfere with the shot string that, further, is sufficiently robust to withstand handling and engagement with a ribbed shot sleeve.